Many office products such as computer printers and plotters, plain paper facsimile machines, and photocopiers use mechanisms that transfer a single sheet of pre-cut printing medium (for example, a sheet of paper of a particular size such as 81/2.times.11 letter, 81/2.times.14 legal, or A-4 (metric), or transparencies, or envelopes) from a replenishable supply stack to the hard copy producing apparatus. These mechanisms are commonly referred to as "sheet feeders."
Sheet feeders usually are provided with an adjustable or replaceable media cartridge, tray, or other type of stacker in which a user can stack multiple cut-sheets of a media of choice. The use of media cartridges (essentially easily substituted paper trays) adapted to the various styles and sizes of media provide a mechanism for quick changes between any particular printing medium chosen by the user.
Upon receiving a media feed command from a host computer or the hard copy machine controller electronics (exemplary "FEED command" hereinafter), a sheet picking and transferring subsystem of the sheet feeder is actuated to deliver the top sheet from the stack to the hard copy machine. Under proper operating conditions, a sheet picking and transferring mechanism associated with the stacker should deliver a single sheet of the print medium to a hard copy machine input mechanism, such as a set of pinch rollers used for registration and feed of a single sheet into the actual printing station of the machine.
Misfeeds, multiple sheet picks, paper jams, and the like, are common problems associated with sheet feeders.
Therefore, there is a need to facilitate the transfer of a sheet of print media from a stack picking and transferring subsystem associated with the sheet feeder to a hard copy machine input mechanism.